add isArithmetic concept

Author: SizzinSeal

include/units/units.hpp

@@ -131,6 +131,10 @@ void quantityChecker(Quantity<Mass, Length, Time, Current, Angle, Temperature, L
 template <typename Q>
 concept isQuantity = requires(Q q) { quantityChecker(q); };
 
+// isArithmetic concept
+template <typename T>
+concept isArithmetic = std::is_arithmetic_v<T>;
+
 // Isomorphic concept - used to ensure unit equivalency
 template <typename Q, typename... Quantities>
 concept Isomorphic = ((std::convertible_to<Q, Quantities> && std::convertible_to<Quantities, Q>) && ...);